1. Field of the Invention
The present invention relates to an electrical connector assembly, and more particularly, to an electrical connector assembly with wafers floatably arranged thereon.
2. Description of the Prior Art
U.S. Pat. No. 5,722,848 issued to Lai on Mar. 3, 1998 discloses a typical connector socket, and which is generally referred to as Zero Insertion Force (ZIF) socket. In generally, the socket generally includes a base with a plurality of contacts assembled therein, and a cover moveably attached to the base. A lever along with a cam mechanism is arranged between the base and cover so as to drive the cover from a first position to a second position. When the lever is located in a vertical position, the cover is located at the first position, in which a hole in the cover is completely in align with a corresponding passageway in the base. In this position, a pin leg of a Central Process Unit (CPU) can be inserted from the cover into the passageway without any engagement with the contact. When the CPU is properly seated on the cover, then the lever is moved from the vertical position to a horizontal position, and simultaneously driving the cover from the first position to the second position. During this process, the pin leg of the CPU is then in contact with the contact within the base.
U.S. Pat. No. 7,001,197 issued to Shirai on Feb. 21, 2006 discloses another type of connector socket, and which can be generally called Land Grid Array (LGA) socket. As clearly shown in Figures, the socket generally includes a metal stiffener with a housing securely supported therein. Then a metal clip is pivotally assembled to the stiffener. On the other hand, a clip is pivotally assembled to the other side of the stiffener and when the clip is closed to the stiffener, the lever having a cam can lock the clip to a closed position. By this arrangement, if before the clip is closed, and a CPU is seated on the housing, then the clip will tightly press the CPU toward the housing ensuring proper electrical connection therebetween.
In design the Lai and Shirai sockets, one of the factors, coefficient of thermal expansion (CTE), mismatch is a key factor which may materially effect the design and performance of the socket. As a matter of fact, a CTE of a printed circuit board, and a CTE of socket are different from each other. When the CPU become more and more powerful, heat generated thereon become more and more higher, and the CTE mismatch is really an issue for the designer.
U.S. Pat. No. 6,679,707 issued to Brodsky et al, discloses another configuration of connector socket for interconnecting a CPU to a printed circuit board. In Lai and Shirai disclosures, solder or solder ball are applied, while in Brodsky's disclosure, no solder has been applied. It is generally called LGA-LGA type, or compression type. Since no solder is applied to a contact tail, the contact can move along with the housing. Accordingly, this can reduce the issue of CTE mismatch.
Since the CPU become more and more powerful, input and output ports are increased as well. For a typical Socket 478, it has four hundred seventy-eight contacts. For a Socket T, which is a main trend of the CPU socket available to the market nowadays, it has seven hundred seventy-five contact terminals. In some server application, the contact terminals have exceed one thousand, even exceed seven thousand.
When dealing such a huge amount of contact terminals, it would be impractical to put them all into a single housing in view of CTE mismatch, contact tails coplanarity, etc. As a result, the housing is divided into different units or sections. As disclosed in the Brodsky '707 patent, the housing is divided into four sections, and each interconnected with each other. As discussed above, Brodsky discloses a LGA-LGA type contact, CTE mismatch is not a material issue. If the industry intends to adopt Bordsky's configuration for Lai and Shirai socket, in which solder or solder balls are applied, then CTE mismatch is a grave concern.